Waquar:
I have not posted to you before through lack of intertest in your posts. Your post relates to the 8051 only because you wish to use an 8051. It is in fact a post on basic interfacing and engineering methods. First define your problem. Second determine what data or inputs you need to solve your problem. third find out how to aquire, condition or otherwise manipulate these inputs. By this point you should have a method that will solve (at least you think it will) your problem. Next build and test each required input conditioner and each output load driver required. When that all works then tackle the remaining central portion. Come here and ask only 8051 related questions, demonstrate in your posts that you have done some thinking about solutions and you MAY get help from the professional core group that make this forum so great. If you do not understand why logical methods are used then as has been suggested before perhaps you have chosen the wrong career Terry